<!DOCTYPE html>
<script>
if (window.internals)
    internals.settings.setPreferCompositingToLCDTextEnabled(true);
</script>
<style>
#overflow-clip {
    position: absolute;
    z-index: 0;
    overflow: scroll;
    left: 100px;
    top: 100px;
    width: 300px;
    height: 200px;
    background-color: yellow;
}

#bloat {
    height: 1000px;
}

#squashing {
    position:fixed;
    left: 0;
    top: 0;
}

#squashed {
    position:fixed;
    z-index:1;
    left: 0;
    top: 0;
    right: 0;
    bottom: 0;
    background-color: green;
}
</style>
<div id="overflow-clip">
    <div id="bloat"></div>
    <div id="squashing">You shouldn't see this line or a yellow block.</div>
</div>
<div id="squashed">
    This test suceeds if you only see this line with a green background.
</div>
